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Handle more cases of cast-of-cast in more general forms. 

llvm-svn: 3347
This commit is contained in:
Chris Lattner 2002-08-15 16:15:25 +00:00
parent 8d1118fd8f
commit 3732acab85
1 changed files with 35 additions and 8 deletions
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43
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
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@ -501,20 +501,47 @@ static inline bool isEliminableCastOfCast(const CastInst &CI,
// Allow free casting and conversion of sizes as long as the sign doesn't
// change...
if (isCIntegral(SrcTy) && isCIntegral(MidTy) && isCIntegral(DstTy) &&
SrcTy->isSigned() == MidTy->isSigned() &&
MidTy->isSigned() == DstTy->isSigned()) {
// Only accept cases where we are either monotonically increasing the type
// size, or monotonically decreasing it.
//
if (isCIntegral(SrcTy) && isCIntegral(MidTy) && isCIntegral(DstTy)) {
unsigned SrcSize = SrcTy->getPrimitiveSize();
unsigned MidSize = MidTy->getPrimitiveSize();
unsigned DstSize = DstTy->getPrimitiveSize();
if (SrcSize <= MidSize && MidSize <= DstSize)
return true;
// Cases where we are monotonically decreasing the size of the type are
// always ok, regardless of what sign changes are going on.
//
if (SrcSize >= MidSize && MidSize >= DstSize)
return true;
// If we are monotonically growing, things are more complex.
//
if (SrcSize <= MidSize && MidSize <= DstSize) {
// We have eight combinations of signedness to worry about. Here's the
// table:
static const int SignTable[8] = {
// CODE, SrcSigned, MidSigned, DstSigned, Comment
1, // U U U Always ok
1, // U U S Always ok
3, // U S U Ok iff SrcSize != MidSize
3, // U S S Ok iff SrcSize != MidSize
0, // S U U Never ok
2, // S U S Ok iff MidSize == DstSize
1, // S S U Always ok
1, // S S S Always ok
};
// Choose an action based on the current entry of the signtable that this
// cast of cast refers to...
unsigned Row = SrcTy->isSigned()*4+MidTy->isSigned()*2+DstTy->isSigned();
switch (SignTable[Row]) {
case 0: return false; // Never ok
case 1: return true; // Always ok
case 2: return MidSize == DstSize; // Ok iff MidSize == DstSize
case 3: // Ok iff SrcSize != MidSize
return SrcSize != MidSize || SrcTy == Type::BoolTy;
default: assert(0 && "Bad entry in sign table!");
}
return false; // NOT REACHED
}
}
// Otherwise, we cannot succeed. Specifically we do not want to allow things